Categories of cortical structure.
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Animals↗
Biomedical subjects
D Purves
Publications and source records attributed to D Purves.
Development of blobs in the visual cortex of macaques.
We have examined the area of the primary visual cortex and the number and size of blobs within it in 10 neonatal and 11 adult rhesus monkeys. The average area of the primary visual cortex (V1) increases from 919 mm2 in newborns to 1,069 mm2 in adult animals (16%). The number of blobs decreases per unit area from an average of 5.2/mm2 at birth to 4.3/mm2 in maturity (18%). As a consequence, the number of blobs remains approximately the same during maturation, at about 4,800/hemisphere. These observations correct a preliminary report on a subset of the animals studied here (Purves and LaMantia: Proc Natl Acad Sci 87:5765, '90), in which it appeared that blob number might increase between birth and maturity. As in other regions of the developing postnatal brain, we found no net loss of modular circuitry.
Animals↗
Differential metabolic and electrical activity in the somatic sensory cortex of juvenile and adult rats.
We have examined relative levels of metabolic and electrical activity across layer IV in the primary somatic sensory cortex (S1) of the rat in relation to regions of differential postnatal cortical growth. Each of several indices used--mitochondrial enzyme histochemistry, microvessel density, Na+/K+ pump activity, action potential frequency, and deoxyglucose uptake--indicate regional variations of metabolic and electrical activity in this part of the brain in both juvenile (1-week-old) and adult (10-12-week-old) animals. At both ages, areas of the somatic sensory map related to special sensors such as whiskers and digital pads showed evidence of the most intense activity. Thus, mitochondrial enzyme staining, blood vessel density, and Na+/K+ ATPase activity were all greatest in the barrels and barrel-like structures within S1, and least in the adjacent interbarrel cortex and the cortex surrounding S1. Multiunit recordings in and around the posteromedial barrel subfield of anesthetized animals also showed that the average ratio of evoked to spontaneous activity was greater in barrels than in the surrounding, metabolically less active cortex. Furthermore, autoradiograms of labeled deoxyglucose accumulation in awake behaving animals indicated systematic differences in neural activity across S1 barrels and barrel-like structures showed more deoxyglucose accumulation than interbarrel, nonbarrel, or peri-S1 cortex. These regional differences in neural activity correspond to regional differences in neocortical growth (Riddle et al., 1992). The correlation of greater electrical activity, increased metabolism, and enhanced cortical growth during postnatal maturation suggests that neural activity foments the elaboration of circuitry in the developing brain.
Action Potentials↗
Diagnosis of the acute ischaemic heart by ion elution from myocardium.
The post-mortem diagnosis of acute myocardial ischaemia may be difficult to establish in the absence of morphological changes in the myocardium or recent coronary thrombosis. Ischaemic cell injury leads to potassium (K) efflux and sodium (Na) influx and, if the blood is still circulating, the K:Na ratio of the tissue falls. In this study, the K:Na ratio was measured by eluting the ions from samples of myocardium and assaying the eluate. The method yields similar results to those obtained by a previous method, in which myocardial samples were homogenized. The K:Na ratios on samples of horizontal slices through the heart were plotted on maps of the slices. A low K:Na ratio corresponded to, but extended beyond, areas where there was morphological evidence of ischaemia. The method is simple and may be of use in routine practice.
Acute Disease↗
Iterated patterns of brain circuitry (or how the cortex gets its spots)
The prominence of repeating patterns of circuitry in the mammalian brain has led to the general view that iterated modular units reflect a fundamental principle of cortical function. Here we argue that these intriguing patterns arise not because the functional organization of the brain demands them, but as an incidental consequence of the rules of synapse formation.
Animals↗
A preliminary investigation of promotion of brain tumours by hexachlorophane in Sprague-Dawley rats transplacentally exposed to N-ethylnitrosourea.
Two-stage carcinogenesis (initiation and promotion) has been demonstrated in various mammalian tissues, but there is no conclusive evidence that it occurs in the nervous system. The present work has investigated the possibility that it might occur in the brain of the rat. Pregnant Sprague-Dawley rats were given an initiating dose (10 mg/kg intravenously (i.v.)) of N-ethylnitrosourea (ENU), which resulted in a low but consistent yield of brain tumours in the offspring. The dose was determined in a prior dose-response investigation. The 'initiated' offspring were treated postnatally with the putative promoter, hexachlorophane, and its ability to increase tumour incidence was examined by standardized step sectioning of the brain from rats killed at 6 months. There was no evidence of promotion of ENU-induced brain neoplasms by hexachlorophane in the rat. The experimental procedure led to a reproducible incidence of glial tumours in the pups.
Animals↗
Growth of the rat somatic sensory cortex and its constituent parts during postnatal development.
We have compared the size and arrangement of the primary somatic sensory cortex (SI) and its constituent parts in juvenile (1 week old) and mature (10-12 weeks old) rats using succinic dehydrogenase histochemistry and digital image analysis. Our goal was to determine whether some regions of the maturing cortex grow more than others. To this end, we examined (1) the growth of barrels and the surrounding (interbarrel) cortex, (2) the growth of the major somatic representations within SI, and (3) the overall growth of SI compared to the neocortex as a whole. With respect to the first of these issues, SI barrels and barrel-like structures grow more than the intervening cortex. The growth of these elements varies according to region: barrels in the head representation more than double in size, whereas the barrel-like structures in the paw representations increase by only about half this amount. The growth of the major somatic representations within SI is also heterogeneous, the representation of the head enlarging to a greater extent than the representations of the paws. Thus, the ratio of the total area of head representation to the combined paw representation is 15% greater in adults than in juveniles. Finally, the primary somatic sensory cortex grows to a somewhat greater extent than the neocortex as a whole. These observations demonstrate that postnatal cortical growth is not uniform; it varies among cortical barrels and the immediately surrounding (interbarrel) cortex, among the representations of different body parts, and between SI and the rest of the neocortex. As an explanation of this differential growth, we suggest that the neuropil of metabolically (and/or electrically) more active cortical regions grows to a greater extent during maturation than that of less active regions.
Aging↗
Vital imaging of glomeruli in the mouse olfactory bulb.
We have monitored the pattern of identified glomeruli in the olfactory bulbs of newborn, juvenile, and adult mice over intervals of several hours to several weeks. Our purpose was to assess the development and stability of these complex units in the mammalian brain. Glomeruli can be observed by vital fluorescent staining and laser-scanning confocal microscopy without causing acute or long-term damage to brain tissue. Repeated observation of bulbs in the same animals between birth and 3 weeks of age showed that this region of the brain develops by progressive addition of these units to the original population. This increment occurs by the genesis of smaller new glomeruli between larger existing ones; no elimination of glomeruli was observed during this process. Finally, no addition (or loss) of glomeruli occurred in adult animals over a 2 week interval; once established, the number, size, and pattern of glomeruli are evidently stable.
Aging↗
Specialized vascularization of the primate visual cortex.
We have analyzed blood vessel distribution in the primary and secondary visual cortices of the squirrel monkey in relation to cortical modules, laminae, and cytoarchitectonic areas. Measurements of microvessel length in tangential sections through the primary visual cortex showed that blobs are more richly vascularized than intervening cortical regions. Thus, the mean total length of microvessel profiles per unit was 42% greater within these cortical modules than within adjacent (interblob) areas. Total microvessel length per unit area in another class of module, the stripes in the secondary visual cortex, was 27% greater than in interstripe regions. Microvessel distribution also varied systematically from layer to layer in the primary visual cortex, being greatest in lamina IVc. Finally, the overall microvessel length per unit area in sections of the primary visual cortex was 26% greater than that in the secondary visual cortex. These observations indicate that the modular, laminar, and regional organization of the primate visual cortex is reflected in the underlying distribution of cortical microvessels. These vascular patterns should be discernable in living animals with vascular contrast agents and appropriate imaging techniques.
Animals↗
Peptidergic transmission in the brain. I. Vasopressin-like signal in the hippocampus.
Studies of the action of arginine vasopressin (AVP) in the rat hippocampal slice have produced a model of the peptide's neural action. AVP excites local circuit inhibitory interneurons and causes consequent inhibition of pyramidal cells that is apparent as a reduction in the amplitude of the evoked population spike in field potential recording. Here we show that applied AVP does the same thing to the evoked population spike in the whole animal. Then we show that stimulation of the source of hippocampampal AVP, the medial amygdaloid nucleus, also inhibits the evoked population spike. Analysis of the synaptic potential indicates that the same mechanisms are employed by exogenously applied and endogenously released peptide. The inhibition can only be obtained by stimulating those brain structures known to project vasopressin fibers to the hippocampus. The stimulus-response characteristics and kinetics of the endogenous signal correspond to the properties of peptidergic signals in simple systems. The results are taken to support a transmitter role for AVP in the rat hippocampus.
Action Potentials↗
Peptidergic transmission in the brain. II. Mediation by a vasopressin-like peptide.
The medial amygdaloid nucleus (AME) sends a projection of fibers containing a peptide similar to arginine vasopressin (AVP) to the rat hippocampus. Electrical stimulation of the AME has an impact on evoked hippocampal field potentials that is identical to the effect obtained by applied AVP in vitro or in vivo. Here we show that the AVP-like peptide released by AME stimulation has action that is blocked by a structural AVP analog. The antagonist specificity suggests that the native transmitter is a peptide similar, but not identical, to AVP. We conclude that the AME projection to the hippocampus satisfies all the criteria for recognition as a central peptidergic system important in the generation of behavior.
Amygdala↗
Numbers of "blobs" in the primary visual cortex of neonatal and adult monkeys.
We have examined the number of "blobs" (cytochrome oxidase-positive cortical modules) in the primary visual cortex (area 17) of infant and adult rhesus monkeys. The density of these iterated circuits--about five per mm2--was not significantly different in three newborn and three mature animals. Measurement of the surface of area 17 in serial sections, however, showed that the total area occupied by the primary visual cortex increases by about 50% during maturation. Based on these measurements, the number of blobs in this species is about 8000 at birth and about 12,000 in maturity. Evidently, these complex functional units are added gradually to the developing primate brain over a period that extends into postnatal life.
Aging↗
Construction of modular circuits in the mammalian brain.
Comparison of seemingly different modular units in the mammalian brain raises the possibility of a common mechanism for their formation: the growth of neuropil mediated by trophic interactions. The ongoing postnatal construction of modular circuits according to trophic interplay may in turn account for the remarkable plasticity of the juvenile brain. By the same token, the normal waning of circuit construction during postnatal development may explain the end of critical periods, the diminished ability to recover from injury in older animals, and the decline with increasing age in the ability of mammals to learn complex skills.
Animals↗
Postnatal construction of neural circuitry in the mouse olfactory bulb.
We have undertaken a quantitative analysis of the mouse olfactory bulb to address several major questions concerning the development of neural circuitry in the postnatal mammalian brain. These are: (1) To what degree are new elements and circuits added during maturation? (2) How long do such processes go on? and (3) Does postnatal development involve a net addition of circuits and their constituent elements, or is there elimination of some portion of an initial surfeit? Using male mice of known age, weight, and length, we measured the overall size of the bulb, the numbers of processing units (glomeruli) within the bulb, the extent and complexity of postsynaptic dendrites within the glomeruli, and the number of synapses in different regions of the bulb. Between birth and the time mice reach sexual maturity at 6-7 weeks of age, the bulb increases in size by a factor of 8, the number of glomeruli by a factor of 4-5, the length of mitral cell dendritic branches by a factor of 11, and the number of glomerular and extraglomerular synapses by factors of 90 and 170, respectively. Each of these parameters increases steadily from birth, in concert with the enlargement of the olfactory mucosa, the overall growth of the brain, and indeed, of the entire animal. We found no evidence of an initial surfeit of processing units, dendritic branches, or synapses. Further elaboration of neural circuitry by each of these measures is also apparent from the time of sexual maturity until the animals reach their full adult size at about 10-12 weeks of age. The developmental strategy in this part of the mouse brain evidently involves prolonged construction that persists until the growth of the body is complete. This ongoing elaboration of neural circuitry in the postnatal mammalian brain may be relevant to understanding a number of unexplained developmental phenomena, including critical periods, the ability of the juvenile brain to recover from injuries that would cause severe and permanent deficits in older animals, and the special ability of the maturing brain to encode large amounts of new information.
Aging↗
Development of glomerular pattern visualized in the olfactory bulbs of living mice.
Many regions of the mammalian brain are characterized by iterated ensembles of nerve cells which can be distinguished anatomically and physiologically. A particularly striking example is the pattern of glomeruli in the olfactory bulbs; other instances are columns and 'blobs' in the visual cortex, barrels and columns in the somatosensory cortex, and striasomes and cell islands in the neostriatum. Understanding the generation of these neuronal ensembles has a bearing on a variety of important neurobiological problems, including the nature of critical periods, the age-dependent response of the nervous system to injury and the manner in which neural information is stored. Analysis of these issues has usually been restricted to studies of the brains of different individuals at various ages. Many questions about the formation of such units, however, can only be answered by observing the same brain repeatedly in a living animal. This strategy would enable a direct assessment of how these units are assembled, whether the initial ensembles persist and whether units are lost or gained as an animal matures. We have succeeded in studying the pattern of glomeruli in the mouse olfactory bulb on two separate occasions during postnatal development. Comparison of the patterns observed at intervals of up to three weeks show that this part of the brain is gradually constructed by the addition of new glomeruli to a persisting population.
Age Factors↗
Ongoing electrical activity of superior cervical ganglion cells in mammals of different size.
The ongoing synaptic activity of superior cervical ganglion cells in adult mammals was examined in situ by intracellular recording in anesthetized mice, hamsters, rats, guinea pigs, and rabbits. The proportion of neurons exhibiting subthreshold and suprathreshold synaptic activity during a standard period of observation was least in a small mammal like the mouse (30%), intermediate among neurons of mammals of intermediate size such as the hamster and rat (48% and 45%, respectively), and greatest in the largest animals in the series, the guinea pig (89%) and rabbit (91%). Ganglion cells in all species fell silent after transection of the cervical trunk. The average frequency of synaptic activity among tonically active cells also increased with animal size, being least in the mouse (1.0/second) and greatest in the rabbit (6.4/second). This variation of ongoing synaptic activity in sympathetic ganglion cells may reflect the demands of progressively larger peripheral targets on relatively fixed populations of autonomic neurons.
Action Potentials↗
Assessing some dynamic properties of the living nervous system.
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Animals↗
Rapid remodeling of sensory endings in the corneas of living mice.
The terminals of trigeminal neurons were followed over time in the corneas of living mice by repeated staining with a nontoxic fluorescent dye. The purpose of these observations was to evaluate remodeling of sensory nerve endings in an adult mammal. Video images of topically stained nerve endings within particular corneal regions were recorded initially, and then again after intervals ranging from 4 hr to 30 d. Comparison of the 2 sets of images showed that sensory endings in the corneal epithelium undergo continual rearrangement under normal circumstances. Substantial changes in terminal configuration occurred over periods as brief as a day.
Animals↗